1. Field of the Invention
The present invention relates generally to electrical power distribution, and more particularly, to balanced transforming and distributing of electrical power through a plurality of circuits to provide safety and reliability.
2. Description of the Related Art
Electrical power is universally conveyed through power grids in alternating current (AC) form. Transformers are required to either step up or step down the transmitted power for various applications. For example, for common usage through a single electrical outlet, electrical power is transmitted at a voltage level of between 115 V (Volt) and 120 V alternating at a frequency of 60 Hz (Hertz) with a current limit of 16 A (Ampere). The current limit of 16 A per outlet is set by the NFPA (National Fire Protection Association) for safety reasons. To operate appliances or machines which exceed the set limit, power must be withdrawn from a poly-phase system. Installations of poly-phase systems are costly and heretofore have been mostly confined to industrial sites. Accordingly, heavy-duty power usages through single-phase outlets are very often impractical for almost all purposes as explained below.
To operate a heavy-duty load under a single-phase power delivery environment, one possible scheme is to withdraw power from more than one outlets simultaneously. This practice is fraught with danger. FIG. 1 shows such configuration. It should be noted that the scheme shown in FIG. 1 has not been known to have been attempted by others and is presented herein only for purpose of illustration. Suppose a load 2 operates at a power level of 3 KW (Kilo-Watts). Without any three-phase outlet, power may be drawn from single-phase outlets 4 and 6. Further suppose that the outlet 4 or 6 supplies power at a voltage level of 115 V with a current limit of 16 A. Assuming 115 V and 16 A are expressed in root-mean-square values. Thus maximum power that can be withdrawn from either the outlet 4 or 6 is 1.84 KW (115 V.times.16 A), well below the required 3 KW. To meet the demand, a possible approach is to extract power simultaneously from the two outlets 4 and 6.
Shown in FIG. 1 is an arrangement in which two circuits 5 and 7 withdraw power simultaneously from two separate single-phase outlets 4 and 6. Thereafter, the outputs of the circuits 5 and 7 are merged together to supply power to a single load 2.
To begin with, attention is directed to the first circuit 5, in which a transformer 8 is disposed between the outlet 4 and a rectifier 10. Power is transmitted to the rectifier 10 from the outlet 4 via the transformer 8. After passing through the half-wave rectifier 10, the extracted power is directed to a power factor correction circuit 12. The function of the power correction circuit 12 is to align the supply voltage to be as much in phase with the resultant current as possible such that the supplied power is maximally utilized. Thereafter, the power reaches the intended load 2.
For the second circuit 7 extracting power from the outlet 6, the arrangement is substantially the same as that for the circuit 5 and is thus not further repeated.
The pitfall with the power distributing arrangement as shown in FIG. 1 is that one distributing circuit, which can either be circuit 5 or 7, may withdraw a higher current level in comparison to the other. The skew current distribution may be caused by manufacturing tolerances of components made up of the circuits 5 and 7. Alternatively, the skew current distribution may also be caused by other ambient factors such as temperature variations, or even different physical placements of the circuits with different wiring lengths. When the power exceeds the rated amount for any of the outlets 4 or 6, the circuit breaker or fuse associated with the circuit outlet 5 or 6, if operational, will be tripped or blown. As a consequence, there will be a complete power shutoff from either one of the outlets 4 or 6. Once that occurs, the other circuit 5 or 7 carries the burden of supplying the entire power demand. Since it is assumed that the entire power demand exceeds the rated power limit of each outlet 4 or 6, the protective mechanism of the remaining outlet is triggered into action also resulting in another complete power shutoff to the remaining circuit. Consequently, the operation of the load 2 will be unexpectedly turned off. For the aforementioned reasons, the operation of the load 2 is highly unpredictable and is at the mercy of whether there are matched current flows through the circuits 5 and 7. Accordingly, withdrawing large amount of power from multiple single-phase outlets and simultaneously driving a single load are seldom attempted.
Because of the high costs associated with installation of poly-phase power transmission systems, in most areas, such installations are confined to industrial sites for the purpose of powering heavy-duty machinery. However, there have been increasing demands for high power usages beyond the industrial sites. For instance, technological advances in telecommunications and data networks have progressed rapidly in recent years. Installations of these telecommunications or data networks are very often in office buildings with only single-phase outlets. Powering up such networks require considerable electrical power in which single-phase outlets may not be capable of meeting the rating requirements. Rewiring an existing office building with poly-phase power outlets is an expensive undertaking.
In addition to the problem encountered above, in powering a heavy-duty load, there is also a need to assure high reliability in the powering process. For instance, in the same example as mentioned before in which an extensive piece of telecommunications network equipment needs to be operated, in particular applications, operational reliability is of paramount importance. For example, the equipment may transact instantaneous on-line financial data and any failure, such as power related failure, may cause disastrous consequences. Without expensive alteration to existent power outlets, there has been a long-felt need to provide solutions to tackle the aforementioned problems.